(a) Field of the Invention
The present invention relates to an organic electroluminescence display panel.
(b) Description of the Related Art
Generally, an organic electro-luminescence (EL) display is a self emissive display device, which displays images by exciting an emissive organic material to emit light. The organic EL display includes an anode (hole injection electrode), a cathode (electron injection electrode), and an organic light emission layer interposed therebetween. When the holes and the electrons are injected into the light emission layer, they are recombined and pair annihilated with emitting light. The light emission layer further includes an electron transport layer (ETL) and a hole transport layer (HTL) as well as an electron injecting layer (EIL) and a hole injecting layer (HIL) for enhancing the light emission.
A plurality of pixels of the organic EL display, each including an anode, a cathode, and a light emission layer, are arranged in a matrix and driven in passive matrix (or simple matrix) addressing or active matrix addressing.
The passive matrix type organic EL display includes a plurality of anode lines, a plurality of cathode lines intersecting the anode lines, and a plurality of pixels, each including a light emission layer. The selection of one of the anode lines and one of the cathode lines cause light emission of a pixel located at the intersection of the selected signal lines.
The active matrix type organic EL display includes a plurality of pixels, each including a switching transistor, a driving transistor, and a storage capacitor as well as an anode, a cathode, and a light emission layer. The EL display further includes a plurality of gate lines transmitting gate signals and a plurality of data lines transmitting data voltages. The switching transistor is connected to one of the gate lines and one of the data lines and transmits the data voltage from the data line in response to the gate signal. The driving transistor receives the data voltage from the switching transistor and drives a current having a magnitude determined depending on the difference between the data voltage and a predetermined voltage such as a supply voltage. The current from the driving transistor enters the light emission layer to cause light emission having an intensity depending on the current. The storage capacitor is connected between the data voltage and the supply voltage to maintain their voltage difference. The gray scaling of the active matrix type EL display is accomplished by controlling the data voltages to adjust the current driven by the driving transistor. The color representation of the EL display is obtained by providing red, green and blue light emission layers.
In the meantime, the decrease of the supply voltage reduces the current driven by the driving transistors such that the displayed image is darker than is expected. For example, the data voltages with higher magnitude for displaying higher grays experience higher voltage drop such that the reduction of the currents driven by the driving transistors is much severer. The smaller currents makes the pixels associated therewith emit darker lights, thereby generating cross-talk, which becomes severer as the number of the pixels expected to emit bright lights is increased.